The present invention relates to a process for the complete working up of concentrates, containing Cu, Zn, Ag, and possibly Au, in particular, by means of combined extraction and leaching processes.
During the past years the hydrometallurgical working up of copper concentrates as well as of complex copper-zinc concentrates has increasingly gained in importance. In comparison with pyrometallurgical processes, these hydrometallurgical ones have the advantages of higher flexibility and selectivity and, frequently, also of higher non-ferrous metal yields. What is of great weight is the fact that they are favorable to the environment.
These hydrometallurgical processes can be divided into three categories, viz. direct leaching, leaching after activating pretreatment, and leaching after sulfatizing (disintegrating) roasting. In each case there is obtained a metal solution, worked up in known manner to its non-ferrous metals or their salts, and a leaching residue. As extraction never is a hundred percent, these residues partially contain considerable amounts of non-ferrous metals, and, in particular, they always contain the whole, or almost the whole, of the original (primary) precious metal contents.
Relatively little is reported on the working up of leaching residues in the numerous publications in the art and in the numerous patents dealing with the various hydrometallurgical extraction processes. If there is any reference at all, it is to the recovery of the valuable constituents in the residues preferably by means of flotation and/or cyanide leaching. Generally speaking, the yields, thus obtained, are unsatisfactory.
Thus, for example, there was obtained by means of ammonia pressure extraction of a copper-zinc ore (see Canad. Mining Metallurg., Bull. 1964, Aug., pp. 857-866) a leaching residue that contained the whole of the silver and gold as well as 4.4 percent of the original (primary) copper contents. The precious metal yield, obtained by different techniques of cyanide leaching was within a range of 55-66% of the silver and 27-88% of the gold.
In the extraction of various sulfide copper concentrates after ammonia leaching under normal pressure, known in the literature of the art as the Arbiter process (see Kuhn, M. C., N. Arbiter and H. Kling: Anaconda's Arbiter Process for Copper, Paper to Hydrometallurgy Sect. of the CIM, Oct. 1, 1973, in Edmonton, Canada), flotation of the leaching residues made it possible for a total yield to be obtained of about 70-90% of the silver and 96-97% of the copper.
Both processes, mentioned above, belong to the category of direct leaching techniques. Their development has reached the state of pilot plants; a commercial plant, which is to be operated in accordance with the Arbiter process, is under construction.
In the extraction of a copper-zinc concentrate by means of sulfatizing (disintegrating) roasting in a fluidized bed reactor and subsequent leaching with diluted sulfuric acid in a plant with a throughput of 2,400 tons per month of concentrate (see Transactions AIME 203 (1955), Aug., pp. 634-638), there remained in the leaching residue 6% of the copper and 12% of the original (primary) zinc contents in addition to the whole of the precious metal content. By means of flotation of the residue it was possible for 20% of its gold content, 60% of its silver content, 30% of its copper content, and 60% of its zinc content to be separated. The flotation concentrate was conveyed into a copper shaft furnace for the purpose of recovering the copper and precious metals contained. There is also a description of the working up of a copper concentrate by means of sulfatizing roasting with an addition of lime for the purpose of preventing an emission of SO.sub.2 (see Mining Engng. 1972, June, p. 52). Leaching of the roasted material with diluted sulfuric acid having been effected, there remain in the residue the whole of the precious metal content as well as 1.4% of the copper. By means of the cyanide leaching, the gold was almost completely extracted, with only 49% of the silver and none of the copper being extracted. This research work was done on a laboratory scale only.
A completely different process for working up the residue is suggested in another publication (see Griffith, W. A. et al: Development of the Roast-Leach-Electrowin Process for Lakeshore; Paper A 73-64 to AIME 1973 Annual Meeting). In a 5-ton-per-day pilot plant, chalcopyrite was was extracted by means of sulfatizing roasting. On an average, 3.8% of the copper remained in the leaching residue as did the precious metals. The leaching residue was then reduced with the aid of carbon to sponge iron which was used for the cementation of the copper obtained from the direct leaching of oxide ores; thus, the valuable constituents, contained in the residue, are conveyed into the cement copper. There are no data on the yield thus obtained. The process appears to have been especially developed for the simultaneous working up of oxide and sulfide copper ores, i.e. it cannot be applied generally. Moreover, it appears to be rather expensive and complicated.
The working up of sulfide non-ferrous metal concentrates by means of sulfatizing (disintegrating) roasting in a fluidized bed reactor with subsequent non-ferrous metal extraction by means of acid leaching, which is described in the three last-mentioned examples of the level reached by the technology, has come to be very widely used on a commercial scale.
Generally speaking, as a compilation of the hydrometallurgy of copper concentrates has it (see Dasher, J., Hydrometallurgy for Copper Concentrates, Paper to 2nd Hydrometallurgy Group Meeting, Canadian Institute of Mining and Metallurgy, CIL House, Montreal, Oct. 2-3, 1972), up to 97% of the non-ferrous metals can be extracted with the aid of acid subsequent to sulfatizing roasting, with the precious metals normally remaining in the leaching residue.
In a survey of the known hydrometallurgical processes for the working up of copper concentrates and of the stage of development, reached in 1972, the difficulty of recovering precious metals from the leaching residues is also pointed out (see Canad. Metallurg. Quart. 11 (1972) 2, pp. 387-400). All the processes, mentioned above as examples, also make it clear that the working up of the leaching residues to recover the residual non-ferrous and precious metals can only be effected in an unsatisfactory manner.
The concentrates treated in the process of the invention are copper concentrates, copper-zinc concentrates and copper-zinc-lead concentrates.